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------------------------------- 2753 - UNIVERSE - how big is it?
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- Our deepest astronomy photos show ultra-distant quasars and galaxies whose redshifts indicate their light has traveled for nearly 13 billion years. Thus, they are 13 billion light-years away? And that must define the edge of the ‘visible universe“?
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- That figure only tells us how long an object’s light has been traveling. It’s not the end of the story, because ever since a given galaxy emitted the light we’re now seeing, it’s been zooming away from us. Today that galaxy is 46 billion light-years distant.
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- How could anything reach a distance of 46 billion light-years in the mere 13 billion years since it emitted the light we now see? That would mean it’s currently receding faster than light. Or that space is so warped we’re not viewing it correctly.
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- Faster-than-light recession doesn’t violate relativity in this case because the galaxy’s mass was never accelerated. It’s merely the intervening empty space between galaxies that has been wildly inflating, which makes the real radius of the observable universe very nearly 46 billion light-years.
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- Light from objects any farther away will never get here because space’s expansion will stretch out and weaken, and we will out-race their rays. So, it’s a real boundary beyond which there is eternal blankness. We use the term “visible universe” for everything nearer, which is everything we can ever possibly know about.
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- Given the average density of space which is five atoms per cubic yard the visible universe must contain 10^56 tons of matter. And, 10^84 photons of light. At least that is what physicists calculate. Take 1 and follow it with 84 zeros and you will see how big a number this is.
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- What about the universe beyond the part we can see? The real universe? How big is the whole thing? There’s no sign that galaxy clusters get any sparser as we approach the edge of the observable universe.
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- After charting 900,000 galaxies astronomers have shown that the topology of the visible universe is perfectly flat, which means stuff keeps abundantly going on beyond the visible boundary.
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- One theory, using the most plausible figures for when the era of inflation began just after the Big Bang, concludes that the overall universe is 300 billion trillion times larger than the visible universe. But it’s also possible the real universe is infinite, which is even larger.
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- An unbounded finite universe could be bending of space-time along its circumference to permit galaxy light to circle around. We earthly observers could see a second image of a nearby galaxy. That duplicate observation would be of the galaxy’s far side after its light had circled the cosmos.
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- It would probably be unrecognizable as the same object, since we’d be seeing it in the distant past, at an earlier stage of its evolution. But if there’s a bunch of such duplicates out there, then the cosmos is smaller than it seems. Which is it?
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- When we are trying to see the edges of the Universe not only does a universal constant of expansion seem annoyingly inconstant at the outer fringes of the cosmos, it occurs in only one direction. The “cosmological constant” is not so constant after all.
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- The “fine structure constant” is the quantity that physicists use as a measure of the strength of the electromagnetic force. It is a dimensionless number and it involves the ratio of the speed of light, Planck's constant, and the electron charge. It is the number that physicists use to measure the “strength of the electromagnetic force“.
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- The electromagnetic force is what keeps electrons whizzing around a nucleus in every atom of the universe. Without it, all matter would fly apart. Up until recently, it was believed to be an unchanging force throughout time and space. A force that is the same everywhere.
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- However, astronomers have noticed anomalies in the fine structure constant whereby electromagnetic force measured in one particular direction of the universe seems ever so slightly different than in the opposite direction.
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- They have also found that that number of the fine structure constant was different in certain regions of the universe. Not just as a function of time, but actually also in ‘direction” in the universe.
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- The most distant quasars that we know of are about 12 to 13 billion light years from away. If we study the light in detail from distant quasars, we are studying the properties of the universe as it was when it was in its infancy, only a billion years old. The universe then was very, very different. No galaxies existed, the early stars had formed but there was certainly not the same population of stars that we see today. And there were no planets.
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- Studying one such quasar enabled astronomers to probe back to when the universe was only a billion years old which had never been done before.
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- They made four measurements of the fine structure constant along the one line of sight to this quasar. Individually, the four measurements didn't provide any conclusive answer as to whether or not there were perceptible changes in the electromagnetic force. However, when combined with lots of other measurements between this measurement and distant quasars measurements made by other scientists, the differences in the fine structure constant became evident.
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- The results seem to be supporting this idea that there could be a directionality in the universe. So, the universe may not be “isotropic” in its laws of physics, one that is the same, statistically, in all directions.
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- There could be some direction or preferred direction in the universe where the laws of physics change, but not in the perpendicular direction. In other words, the universe in some sense, has a dipole structure to it.
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- In one particular direction, we can look back 12 billion light years and measure electromagnetism when the universe was very young. Putting all the data together, electromagnetism seems to gradually increase the further we look, while towards the opposite direction, it gradually decreases.
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- In other directions in the cosmos, the fine structure constant remains constant. These new very distant measurements have pushed our observations further than has ever been reached before.
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- In what was thought to be an arbitrarily random spread of galaxies, quasars, black holes, stars, gas clouds and planets (with life flourishing in at least one tiny niche of it) the universe suddenly appears to have the equivalent of a north and a south.
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- Observations about X-rays that seemed to align with the idea that the universe has some sort of directionality. Thee observations are not testing the laws of physics, they're testing the properties, the X-ray properties of galaxies and clusters of galaxies and cosmological distances from Earth.
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- They also found that the properties of the universe in this sense are not isotropic and there's a preferred direction. Their direction coincides with the fine structure data.
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- Faster-than-light recession doesn’t violate relativity in this case because the galaxy’s mass was never accelerated. It’s merely the intervening empty space between galaxies that has been wildly inflating, which makes the real radius of the observable universe very nearly 46 billion light-years.
-
- Light from objects any farther away will never get here because space’s expansion will stretch out, weaken, and out-race their rays. So, it’s a real boundary beyond which there is eternal blankness. We use the term “visible universe” for everything nearer, which is everything we can ever possibly know about.
-
- What about the universe beyond the part we can see? The real universe? How big is the whole thing?
-
- There’s no sign that galaxy clusters get any sparser as we approach the edge of the observable universe. A study charted 900,000 galaxies to show that the topology of the visible universe is perfectly flat, which means stuff keeps abundantly going on beyond the visible boundary.
-
- One theory, using the most plausible figures for when the “era of inflation” began just after the Big Bang, concludes that the overall universe is 300 billion trillion times larger than the visible universe.
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- But it’s also possible the real universe is infinite. If that’s true, galaxies go on and on without end. Results do indeed permit an infinite universe. But because you can never prove infinity, it’ll remain an open question.
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- If the results are wrong, then a much different scenario is also on the table. Before those data, in fact, it seemed that the real cosmos could even be smaller than the visible universe! In an unbounded finite universe, the bending of space-time along its circumference would permit galaxy light to circle around.
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- Thus, we earthly observers could see a second image of a nearby galaxy. That duplicate observation would be of the galaxy’s far side after its light had circled the cosmos. It would probably be unrecognizable as the same object, since we’d be seeing it in the distant past, at an earlier stage of its evolution. But if there’s a bunch of such duplicates out there, then the cosmos is smaller than it seems.
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- We started out asking a simple question and ended up nauseated. Now you know why I prefer observing beloved lunar craters like Copernicus and Eratosthenes. They’re 50 miles wide, a known distance away, and none of that is ever going to change.
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- The electromagnetic force is one of those quantities that we depend on. If it were only a few percent different to the value we measure on Earth, the chemical evolution of the universe would be completely different and life may never have got going.
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- It raises a tantalizing question: does this "Goldilocks” situation, where fundamental physical quantities like the fine structure constant are 'just right' to favor our existence, apply throughout the entire universe?"
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- If there is a directionality in the universe, and, if electromagnetism is shown to be very slightly different in certain regions of the cosmos, the most fundamental concepts underpinning much of modern physics will need revision.
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- The standard model itself is built upon Einstein's theory of gravity, which itself explicitly assumes constancy of the laws of Nature. If such fundamental principles turn out to be only good approximations, the doors are open to some very exciting, new ideas in physics."
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- So does this mean that there's something special about where we live? This is a reasonable line of thinking, and it was how modern science got its start. The first astronomers assumed that the sun, moon, planets and stars orbited around the Earth. That the Earth was a very special and unique place, distinct from the rest of the universe.
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- But as astronomers started puzzling out the nature of the laws of physics, they realized that the Earth wasn't as special as they thought. In fact, the laws of nature that govern the forces on Earth are the same everywhere in the universe.
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- As Isaac Newton untangled the laws of gravity here on Earth, he realized it must be the same forces that caused the moon to go around the Earth, and the planets to go around the sun. That the light from the sun is the same phenomenon as the light from other stars.
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- When astronomers consider the universe at the largest scales, they assume that it's homogeneous, and isotropic. When astronomers say the universe is “homogeneous“, this means that observers in any part of the universe will see roughly the same view as observers in any other part. There might be local differences, like our mostly harmless planet Earth, orbiting the future course of an interstellar bypass.
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- At the smallest scales, they'll be different. But as you move to larger and larger scales, it's all just planets, stars, galaxies, galaxy clusters and black holes. And if you unfocus your eyes, it all looks pretty much the same.
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- “Isotropic” means that the universe looks the same in every direction. The cosmic microwave background radiation looks the same in all directions.
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- If the universe wasn't homogeneous and isotropic, then it would mean that the physical laws as we understand them are impossible to comprehend. Just over the cosmological horizon, the force of gravity might act in reverse, the speed of light might be slower than walking speed.
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- While we don't live in a special place in the universe, we do live in a special time in the universe. In the distant future, billions or even trillions of years from now, galaxies will be flying away from us so quickly that their light will never reach us. The cosmic background microwave radiation will be redshifted so far that it's completely undetectable.
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- Future astronomers will have no idea that there was ever a greater cosmology beyond the Milky Way itself. The evidence of the Big Bang and the ongoing expansion of the universe will be lost forever.
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- If we didn't happen to live when we do now, within billions of years of the beginning of the universe, we'd never know the truth.
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- We can't feel special about our place in the universe, it's probably the same wherever you go. But we can feel special about our time in the universe. Future astronomers will never understand the cosmology and history of the cosmos the way you do now after reading this.
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- June 3, 2020 2753
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--------------------- Thursday, June 4, 2020 -------------------------
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